Fuel logs show junk mileage from start

Purchased a 2003 TDI from Navy guy moving to Italy. GLS, 5 speed, no mods when purchased. Long and short is that he drove the thing like a beast for 10 years and didn't change the timing belt. Blew up and fixed it in . Didn't drive it much after that. One thing he did give me when I purchased it was his fuel log. He hand wrote every fill up he did. Over the 15 years of the car, I can only find about 5 purchases he missed. I spent quite a while plugging the numbers into the program to find base line mileage.

Life of car average MPG: 42.60

That said, there were spikes in mileage, but only after driving cross country from San Diego to Connecticut. He made several of these trips and each one showed that from Arizona to (Louisiana, Arkansas, Kansas) he was hitting 52mpg. Before that he was at 38-42mpg. After that he was at 38-42mpg. Each time back and forth (it did not matter which direction) he was hitting 49-52mpg through that area.

I have had the car now since January. There were a lot of basic maintenance stuff that had not been done - fuel - air - cabin filter, vacuum hoses, oil change, etc. That done, it did not improve the mileage. It has improved the performance. I still cannot break 42 no matter how I drive.

My first TDI was a 99.5 stock with the EGR turned off. That thing would climb mountains like a champ and no matter how I drove it would get between 48-52mpg every single day. After 364,000 miles, three timing belts, several tire and oil changes, no modifications, it still got 50mpg.

I know the GLS model is ~500lbs heaver than the base model. Is it the weight or something in the programing for the 02-03 models?

It could be that the PO's driving habits resulted in the kind of FE numbers he recorded, although he'd have to be pretty aggressive to get it that low. And your numbers post repair may depend on how it was repaired, and how well the car is now set up post-repair. "Blew up and fixed it" could mean any number of things.

One place to start would be a compression test. Then look at fuel balance, and fuel logs. Next I'd check timing, both static and programmed, followed by boost logs. Optimizing all these factors will allow you to get better FE.

My average in Fuelly for my '02 Wagon is around 45 MPG. That includes summer and winter driving, commuting, and road trips where I usually run at 75-80 MPH. I can see low 50s at 75 in good weather. You should, too.

42 is pretty normal for stock, it's what mine got
got 46 with a tune, 48 with bigger injectors, and now with a crapload of other stuff done it's still doing 48 oddly enough. Only time it's worse is when towing stuff.

never really been able to drive 'nice' for a full tank